Multicast DNS (mDNS) and DNS Service Discovery (DNS-SD), collectively know as zeroconf, are technologies used for devices to find each other and advertise services on the local network.

There are two widely used FOSS implementations: mDNSResponder is used by Apple and Android, while Avahi is used by most GNU/Linux distributions. However, there is a third one in systemd-resolved -- widely installed but rarely used.

In this talk, I will explain how mDNS and DNS-SD work individually and together, and explore how to use them with resolvectl. I'll also try to go over the deficiencies in the systemd-resolved and have a discussion about the ways that it can be improved to replace Avahi as the default implementation on GNU/Linux systems.